Printhead assembly with removable jetting module

ABSTRACT

An inkjet printhead assembly includes a rail assembly and a removable jetting module. The rail assembly includes a beam and a rod attached to the beam. A printhead module includes the jetting module and a mounting assembly. The jetting module includes an array of nozzles, a first alignment tab having a first alignment datum and a second alignment datum, a second alignment tab having a third alignment datum and a fourth alignment datum, a rotational alignment feature including a fifth alignment datum, and a cross-track alignment feature including a sixth alignment datum. The mounting assembly includes a similar set of alignment features. Portions of the alignment tabs of the jetting module and the mounting assembly are adapted to fit within corresponding notches in the beam and engage with the rod. A jetting module clamping mechanism applies a force to the jetting module causing it to engage with the rail assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly assigned, co-pending U.S. patentapplication Ser. No. 15/163,235, entitled: “Modular printhead assemblywith common center rail”, by J. Brazas et al.; and to commonly assigned,co-pending U.S. patent application Ser. No. 15/163,549, entitled:“Inkjet printhead assembly with repositionable shutter”, by J. Brans etal., each which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention pertains to the field of inkjet printing and moreparticularly to an inkjet printhead assembly including a removablejetting module.

BACKGROUND OF THE INVENTION

In the field of high speed inkjet printing it is desirable to be able toprint across the width of the print media in a single pass of the printmedia past a print station. However, for many applications the desiredprint width exceeds the width of the available printheads. It istherefore necessary to arrange an array of printheads such that eachprinthead in the array prints a print swath, and the set of print swathscover the entire print width. Whenever the printed image is made of aset of print swaths, it is necessary to align or stitch each pair ofadjacent print swaths to each other such that the seam between adjacentprint swaths is not visible.

For such printing applications it is desirable to provide some means toaccurately align the array of printheads relative to each other toprovide consistency in the stitching of the print swaths. Even withimprovements in the reliability of the printheads, it is desirable toprovide means for removing and replacing individual printheads withinthe array of printheads. The structure for aligning the printheads intoan array should therefore enable individual printheads to be removedfrom the array and replaced with another printhead with minimal changein the alignment of the printheads and their corresponding print swaths.

Commonly assigned U.S. Pat. No. 8,226,215 (Bechler et al.) provides astructure for aligning a plurality of printheads, with the printheadsarranged in two staggered rows of printheads. It uses a printheadbaseplate that includes sets of kinematic alignment features, one setfor each printhead, to engage with alignment features on the printheadsin order to provide repeatable alignment of the printheads.

Even with a fixed alignment of the array of printheads there is somevariation in the quality of the stitching. It has been determined thatthe amplitude of the stitching variation depends in part on the spacingbetween the nozzle arrays in the two rows of printheads, with a smallerspacing between the rows yielding less variation in the stitching. Ithas also been found that as the desired print width increases, the costfor manufacturing the alignment baseplate to accommodate the increasedprint width increases significantly. There remains a need to provide animproved alignment system that can more readily accommodate wider printwidths and provide a reduced spacing between the nozzle arrays in therows of printheads.

In the field of continuous inkjet printing, each printhead includes adrop generator, which includes an array of nozzles, and drop selectionhardware, which includes a mechanism to cause, for each of the nozzlesin the array, the trajectories of printing drops to diverge from thetrajectories of non-printing drops. An ink catcher is used to interceptthe trajectory of the non-printing drops from each nozzle. It has beenfound that a skew of the drop selection hardware relative to the nozzlearray can contribute to a skew of the images printed by the printheadrelative to the print swaths of other printheads in an array ofprintheads. There remains a need for an improved system for aligning thedrop selection hardware of a printhead relative to the nozzle array of aprinthead.

In the field of continuous inkjet printing, it has been common toprovide a shutter mechanism for sealing an outlet of the printheads toprevent ink from passing through the outlet during startup/shutdown andother maintenance procedures of the printhead. The shutter is thendisplaced from the outlet during the operation mode of the printhead toenable print drops to be emitted through the outlet and deposited ontothe print media. Prior art shutter arrangements have been found to limitthe spacing between printhead rows, and to limit the effectiveness forperforming various maintenance operations. There remains a need for acompact repositionable shutter mechanism.

SUMMARY OF THE INVENTION

The present invention represents an inkjet printhead assembly includinga removable jetting module for printing on a print medium travelingalong a media path from upstream to downstream, including:

a rail assembly spanning the print medium in the cross-track directionincluding:

-   -   a beam; and    -   a rod attached to a side of the beam that faces the print        medium;        a printhead module including:    -   a jetting module having an array of nozzles extending in a        cross-track direction, wherein the jetting module includes:        -   a first alignment tab having a first alignment datum and a            second alignment datum;        -   a second alignment tab having a third alignment datum and a            fourth alignment datum, the second alignment tab being            spaced apart from the first alignment tab in the cross-track            direction;        -   a rotational alignment feature including a fifth alignment            datum; and        -   a cross-track alignment feature including a sixth alignment            datum; and    -   a mounting assembly adapted to engage with the rail assembly at        a defined cross-track position including:        -   a third alignment tab having a seventh alignment datum and            an eighth alignment datum;        -   a fourth alignment tab having a ninth alignment datum and a            tenth alignment datum, the fourth alignment tab being spaced            apart from the third alignment tab in the cross-track            direction;        -   a rotational alignment feature including an eleventh            alignment datum;        -   a jetting module clamping mechanism for applying a force to            the jetting module that causes the first alignment datum,            the second alignment datum, the third alignment datum and            the fourth alignment datum of the jetting module to engage            with the rod, and causes the fifth alignment datum of the            jetting module to engage with corresponding rotational            alignment feature associated with the beam; and    -   a mounting assembly clamping mechanism for applying a force to        the mounting assembly that causes the seventh alignment datum,        the eighth alignment datum, the ninth alignment datum, and the        tenth alignment datum of the mounting assembly to engage with        the rod, and causes the eleventh alignment datum of the mounting        assembly to engage with a corresponding alignment feature on the        beam; and    -   a jetting module cross-track force mechanism for applying a        cross-track force to the jetting module that causes the sixth        alignment datum of the jetting module to engage with a        corresponding cross-track alignment feature associated with the        beam;    -   wherein portions of the first and second alignment tabs of the        jetting module and portions of the third and fourth alignment        tabs of the mounting assembly are adapted to fit within        corresponding notches in the beam.

This invention has the advantage that both the jetting module and themounting assembly can be easily removed and replaced.

It has the further advantage that the printhead assembly is more compactand less expensive to manufacture relative to prior art printheadassemblies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block schematic diagram of an exemplarycontinuous inkjet system according to the present invention;

FIG. 2 shows an image of a liquid jet being ejected from a dropgenerator and its subsequent break off into drops with a regular period;

FIG. 3 shows a cross sectional of an inkjet printhead of the continuousliquid ejection system according to this invention;

FIG. 4 shows a first example embodiment of a timing diagram illustratingdrop formation pulses, the charging electrode waveform, and the breakoff of drops;

FIG. 5 shows a top view of an exemplary printhead assembly including astaggered array of jetting modules;

FIG. 6 shows an exemplary modular printhead assembly including aplurality of printhead modules mounted onto a central rail assembly inaccordance with the present invention;

FIG. 7 illustrates additional details of the rail assembly in themodular printhead assembly of FIG. 6;

FIG. 8 illustrates additional details of the jetting modules in themodular printhead assembly of FIG. 6;

FIGS. 9A-9E illustrate exemplary alignment tab configurations;

FIG. 10 illustrates additional details of the mounting assemblies in themodular printhead assembly of FIG. 6;

FIG. 11 shows a top view of the modular printhead assembly of FIG. 6;

FIGS. 12A-12D show cross-section views of the modular printhead assemblyof FIG. 6;

FIGS. 13A-13B show side views of the modular printhead assembly of FIG.6;

FIG. 14 is an exploded view showing components of a shutter mechanismincluding a repositionable shutter according to an exemplary embodiment;

FIG. 15 shows the assembled components of the shutter mechanism of FIG.14;

FIGS. 16A-16B illustrate the operation of the repositionable shutter ofFIG. 15 using an actuator mechanism; and

FIG. 17A-17B illustrate additional details pertaining to the operationof the repositionable shutter of FIG. 15.

It is to be understood that the attached drawings are for purposes ofillustrating the concepts of the invention and may not be to scale.Identical reference numerals have been used, where possible, todesignate identical features that are common to the figures.

DETAILED DESCRIPTION OF THE INVENTION

The present description will be directed in particular to elementsforming part of, or cooperating more directly with, apparatus inaccordance with the present invention. It is to be understood thatelements not specifically shown or described may take various forms wellknown to those skilled in the art. References to “a particularembodiment” and the like refer to features that are present in at leastone embodiment of the invention. Separate references to “an embodiment”or “particular embodiments” or the like do not necessarily refer to thesame embodiment or embodiments; however, such embodiments are notmutually exclusive, unless so indicated or as are readily apparent toone of skill in the art. The use of singular or plural in referring tothe “method” or “methods” and the like is not limiting. It should benoted that, unless otherwise explicitly noted or required by context,the word “or” is used in this disclosure in a non-exclusive sense.

The example embodiments of the present invention are illustratedschematically and not to scale for the sake of clarity. One of theordinary skills in the art will be able to readily determine thespecific size and interconnections of the elements of the exampleembodiments of the present invention.

As described herein, the example embodiments of the present inventionprovide a printhead or printhead components typically used in inkjetprinting systems. However, many other applications are emerging whichuse printheads to emit liquids (other than inks) that need to be finelymetered and deposited with high spatial precision. As such, as describedherein, the terms “liquid” and “ink” refer to any material that can beejected by the printhead or printhead components described below.

Referring to FIG. 1, a continuous printing system 20 includes an imagesource 22 such as a scanner or computer which provides raster imagedata, outline image data in the form of a page description language, orother forms of digital image data. This image data is converted tohalf-toned bitmap image data by an image processing unit (imageprocessor) 24 which also stores the image data in memory. A plurality ofdrop forming transducer control circuits 26 reads data from the imagememory and apply time-varying electrical pulses to a drop formingtransducers 28 that are associated with one or more nozzles of aprinthead 30. These pulses are applied at an appropriate time, and tothe appropriate nozzles, so that drops formed from a continuous ink jetstream will form spots on a print medium 32 in the appropriate positiondesignated by the data in the image memory.

Print medium 32 is moved relative to the printhead 30 by a print mediumtransport system 34, which is electronically controlled by a mediatransport controller 36 in response to signals from a speed measurementdevice 35. The media transport controller 36 is in turn is controlled bya micro-controller 38. The print medium transport system shown in FIG. 1is a schematic only, and many different mechanical configurations arepossible. For example, a transfer roller could be used in the printmedium transport system 34 to facilitate transfer of the ink drops tothe print medium 32. Such transfer roller technology is well known inthe art. In the case of page width printheads, it is most convenient tomove the print medium 32 along a media path past a stationary printhead.However, in the case of scanning print systems, it is often mostconvenient to move the printhead along one axis (the sub-scanningdirection) and the print medium 32 along an orthogonal axis (the mainscanning direction) in a relative raster motion.

Ink is contained in an ink reservoir 40 under pressure. In thenon-printing state, continuous ink jet drop streams are unable to reachprint medium 32 due to an ink catcher 72 that blocks the stream ofdrops, and which may allow a portion of the ink to be recycled by an inkrecycling unit 44. The ink recycling unit 44 reconditions the ink andfeeds it back to the ink reservoir 40. Such ink recycling units are wellknown in the art. The ink pressure suitable for optimal operation willdepend on a number of factors, including geometry and thermal propertiesof the nozzles and thermal properties of the ink. A constant inkpressure can be achieved by applying pressure to the ink reservoir 40under the control of an ink pressure regulator 46. Alternatively, theink reservoir can be left unpressurized, or even under a reducedpressure (vacuum), and a pump can be employed to deliver ink from theink reservoir under pressure to the printhead 30. In such an embodiment,the ink pressure regulator 46 can include an ink pump control system.The ink is distributed to the printhead 30 through an ink channel 47.The ink preferably flows through slots or holes etched through a siliconsubstrate of printhead 30 to its front surface, where a plurality ofnozzles and drop forming transducers, for example, heaters, aresituated. When printhead 30 is fabricated from silicon, the drop formingtransducer control circuits 26 can be integrated with the printhead 30.The printhead 30 also includes a deflection mechanism 70 which isdescribed in more detail below with reference to FIGS. 2 and 3.

Referring to FIG. 2, a schematic view of continuous liquid printhead 30is shown. A jetting module 48 of printhead 30 includes an array ofnozzles 50 formed in a nozzle plate 49. In FIG. 2, nozzle plate 49 isaffixed to the jetting module 48. Alternatively, the nozzle plate 49 canbe integrally formed with the jetting module 48. Liquid, for example,ink, is supplied to the nozzles 50 via liquid channel 47 at a pressuresufficient to form continuous liquid streams 52 (sometimes referred toas filaments) from each nozzle 50. In FIG. 2, the array of nozzles 50extends into and out of the figure.

Jetting module 48 is operable to cause liquid drops 54 to break off fromthe liquid stream 52 in response to image data. To accomplish this,jetting module 48 includes a drop stimulation or drop forming transducer28 (e.g., a heater, a piezoelectric actuator, or an electrohydrodynamicstimulation electrode), that, when selectively activated, perturbs theliquid stream 52, to induce portions of each filament to break off andcoalesce to form the drops 54. Depending on the type of transducer used,the transducer can be located in or adjacent to the liquid chamber thatsupplies the liquid to the nozzles 50 to act on the liquid in the liquidchamber, can be located in or immediately around the nozzles 50 to acton the liquid as it passes through the nozzle, or can be locatedadjacent to the liquid stream 52 to act on the liquid stream 50 after ithas passed through the nozzle 50.

In FIG. 2, drop forming transducer 28 is a heater 51, for example, anasymmetric heater or a ring heater (either segmented or not segmented),located in the nozzle plate 49 on one or both sides of the nozzle 50.This type of drop formation is known and has been described in, forexample, U.S. Pat. No. 6,457,807 (Hawkins et al.); U.S. Pat. No.6,491,362 (Jeanmaire); U.S. Pat. No. 6,505,921 (Chwalek et al.); U.S.Pat. No. 6,554,410 (Jeanmaire et al.); U.S. Pat. No. 6,575,566(Jeanmaire et al.); U.S. Pat. No. 6,588,888 (Jeanmaire et al.); U.S.Pat. No. 6,793,328 (Jeanmaire); U.S. Pat. No. 6,827,429 (Jeanmaire etal.); and U.S. Pat. No. 6,851,796 (Jeanmaire et al.), each of which isincorporated herein by reference.

Typically, one drop forming transducer 28 is associated with each nozzle50 of the nozzle array. However, in some configurations, a drop formingtransducer 28 can be associated with groups of nozzles 50 or all of thenozzles 50 in the nozzle array.

Referring to FIG. 2 the printing system has associated with it, aprinthead 30 that is operable to produce, from an array of nozzles 50,an array of liquid streams 52. A drop forming device is associated witheach liquid stream 52. The drop formation device includes a drop formingtransducer 28 and a drop formation waveform source 55 that supplies adrop formation waveform 60 to the drop forming transducer 28. The dropformation waveform source 55 is a portion of the mechanism controlcircuits 26. In some embodiments in which the nozzle plate is fabricatedof silicon, the drop formation waveform source 55 is formed at leastpartially on the nozzle plate 49. The drop formation waveform source 55supplies a drop formation waveform 60 that typically includes a sequenceof pulses having a fundamental frequency f_(O) and a fundamental periodof T_(O)=1/f_(O) to the drop formation transducer 28, which produces amodulation with a wavelength λ, in the liquid jet. The modulation growsin amplitude to cause portions of the liquid stream 52 to break off intodrops 54. Through the action of the drop formation device, a sequence ofdrops 54 is produced. In accordance with the drop formation waveform 60,the drops 54 are formed at the fundamental frequency f_(O) with afundamental period of T_(O)=1/f_(O). In FIG. 2, liquid stream 52 breaksoff into drops with a regular period at break off location 59, which isa distance, called the break off length, BL from the nozzle 50. Thedistance between a pair of successive drops 54 is essentially equal tothe wavelength λ of the perturbation on the liquid stream 52. The streamof drops 54 formed from the liquid stream 52 follow an initialtrajectory 57.

The break off time of the droplet for a particular printhead can bealtered by changing at least one of the amplitude, duty cycle, or numberof the stimulation pulses to the respective resistive elementssurrounding a respective resistive nozzle orifice. In this way, smallvariations of either pulse duty cycle or amplitude allow the dropletbreak off times to be modulated in a predictable fashion within±one-tenth the droplet generation period.

Also shown in FIG. 2 is a charging device 61 comprising chargingelectrode 62 and charging electrode waveform source 63. The chargingelectrode 62 associated with the liquid jet is positioned adjacent tothe break off point 59 of the liquid stream 52. If a voltage is appliedto the charging electrode 62, electric fields are produced between thecharging electrode and the electrically grounded liquid jet, and thecapacitive coupling between the two produces a net charge on the end ofthe electrically conductive liquid stream 52. (The liquid stream 52 isgrounded by means of contact with the liquid chamber of the groundeddrop generator.) If the end portion of the liquid jet breaks off to forma drop while there is a net charge on the end of the liquid stream 52,the charge of that end portion of the liquid stream 52 is trapped on thenewly formed drop 54.

The voltage on the charging electrode 62 is controlled by the chargingelectrode waveform source 63, which provides a charging electrodewaveform 64 operating at a charging electrode waveform 64 period 80(shown in FIG. 4). The charging electrode waveform source 63 provides avarying electrical potential between the charging electrode 62 and theliquid stream 52. The charging electrode waveform source 63 generates acharging electrode waveform 64, which includes a first voltage state anda second voltage state; the first voltage state being distinct from thesecond voltage state. An example of a charging electrode waveform isshown in part B of FIG. 4. The two voltages are selected such that thedrops 54 breaking off during the first voltage state acquire a firstcharge state and the drops 54 breaking off during the second voltagestate acquire a second charge state. The charging electrode waveform 64supplied to the charging electrode 62 is independent of, or notresponsive to, the image data to be printed. The charging device 61 issynchronized with the drop formation device using a conventionalsynchronization device 27, which is a portion of the control circuits26, (see FIG. 1) so that a fixed phase relationship is maintainedbetween the charging electrode waveform 64 produced by the chargingelectrode waveform source 63 and the clock of the drop formationwaveform source 55. As a result, the phase of the break off of drops 54from the liquid stream 52, produced by the drop formation waveforms 92,94 (see FIG. 4), is phase locked to the charging electrode waveform 64.As indicated in FIG. 4, there can be a phase shift 108, between thecharging electrode waveform 64 and the drop formation waveforms 92, 94.

With reference now to FIG. 3, printhead 30 includes a drop formingtransducer 28 which creates a liquid stream 52 that breaks up into inkdrops 54. Selection of drops 54 as printing drops 66 or non-printingdrops 68 will depend upon the phase of the droplet break off relative tothe charging electrode voltage pulses that are applied to the to thecharging electrode 62 that is part of the deflection mechanism 70, aswill be described below. The charging electrode 62 is variably biased bya charging electrode waveform source 63. The charging electrode waveformsource 63 provides charging electrode waveform 64, also called acharging electrode waveform 64, in the form of a sequence of chargingpulses. The charging electrode waveform 64 is periodic, having acharging electrode waveform 64 period 80 (FIG. 4).

An embodiment of a charging electrode waveform 64 is shown in part B ofFIG. 4. The charging electrode waveform 64 comprises a first voltagestate 82 and a second voltage state 84. Drops breaking off during thefirst voltage state 82 are charged to a first charge state and dropsbreaking off during the second voltage state 84 are charged to a secondcharge state. The second voltage state 84 is typically at a high level,biased sufficiently to charge the drops 54 as they break off. The firstvoltage state 82 is typically at a low level relative to the printhead30 such that the first charge state is relatively uncharged whencompared to the second charge state. An exemplary range of values of theelectrical potential difference between the first voltage state 82 and asecond voltage state 84 is 50 to 300 volts and more preferably 90 to 150volts.

Returning to a discussion of FIG. 3, when a relatively high levelvoltage or electrical potential is applied to the charging electrode 62and a drop 54 breaks off from the liquid stream 52 in front of thecharging electrode 62, the drop 54 acquires a charge and is deflected bydeflection mechanism 70 towards the ink catcher 72 as non-pint drops 68.The non-printing drops 68 that strike the catcher face 74 form an inkfilm 76 on the face of the ink catcher 72. The ink film 76 flows downthe catcher face 74 and enters liquid channel 78 (also called an inkchannel), through which it flows to the ink recycling unit 44. Theliquid channel 78 is typically formed between the body of the catcher 72and a lower plate 79.

Deflection occurs when drops 54 break off from the liquid stream 52while the potential of the charging electrode 62 is provided with anappropriate voltage. The drops 54 will then acquire an inducedelectrical charge that remains upon the droplet surface. The charge onan individual drop 54 has a polarity opposite that of the chargingelectrode 62 and a magnitude that is dependent upon the magnitude of thevoltage and the coupling capacitance between the charging electrode 52and the drop 54 at the instant the drop 54 separates from the liquidjet. This coupling capacitance is dependent in part on the spacingbetween the charging electrode 62 and the drop 54 as it is breaking off.It can also be dependent on the vertical position of the breakoff point59 relative to the center of the charge electrode 62. After the chargedrops 54 have broken away from the liquid stream 52, they continue topass through the electric fields produced by the charge plate. Theseelectric fields provide a force on the charged drops deflecting themtoward the charging electrode 62. The charging electrode 62, even thoughit cycled between the first and the second voltage states, thus acts asa deflection electrode to help deflect charged drops away from theinitial trajectory 57 and toward the catcher 72. After passing thecharging electrode 62, the drops 54 will travel in close proximity tothe catcher face 74 which is typically constructed of a conductor ordielectric. The charges on the surface of the non-printing drops 68 willinduce either a surface charge density charge (for a catcher face 74constructed of a conductor) or a polarization density charge (for acatcher face 74 constructed of a dielectric). The induced charges on thecatcher face 74 produce an attractive force on the charged non-printingdrops 68. The attractive force on the non-printing drops 68 is identicalto that which would be produced by a fictitious charge (opposite inpolarity and equal in magnitude) located inside the ink catcher 72 at adistance from the surface equal to the distance between the ink catcher72 and the non-printing drops 68. The fictitious charge is called animage charge. The attractive force exerted on the charged non-printingdrops 68 by the catcher face 74 causes the charged non-printing drops 68to deflect away from their initial trajectory 57 and accelerate along anon-print trajectory 86 toward the catcher face 74 at a rateproportional to the square of the droplet charge and inverselyproportional to the droplet mass. In this embodiment the ink catcher 72,due to the induced charge distribution, comprises a portion of thedeflection mechanism 70. In other embodiments, the deflection mechanism70 can include one or more additional electrodes to generate an electricfield through which the charged droplets pass so as to deflect thecharged droplets. For example, an optional single biased deflectionelectrode 71 in front of the upper grounded portion of the catcher canbe used. In some embodiments, the charging electrode 62 can include asecond portion on the second side of the jet array, denoted by thedashed line electrode 62′, which supplied with the same chargingelectrode waveform 64 as the first portion of the charging electrode 62.

In the alternative, when the drop formation waveform 60 applied to thedrop forming transducer 28 causes a drop 54 to break off from the liquidstream 52 when the electrical potential of the charging electrode 62 isat the first voltage state 82 (FIG. 4) (i.e., at a relatively lowpotential or at a zero potential), the drop 54 does not acquire acharge. Such uncharged drops are unaffected during their flight byelectric fields that deflect the charged drops. The uncharged dropstherefore becomes printing drops 66, which travel in a generallyundeflected path along the trajectory 57 and impact the print medium 32to form a print dots 88 on the print medium 32, as the recoding mediumis moved past the printhead 30 at a speed V_(m). The charging electrode62, deflection electrode 71 and ink catcher 72 serve as a drop selectionsystem 69 for the printhead 30.

FIG. 4 illustrates how selected drops can be printed by the control ofthe drop formation waveforms supplied to the drop forming transducer 28.Section A of FIG. 4 shows a drop formation waveform 60 formed as asequence that includes three drop formation waveform 92, and four dropformation waveforms 94. The drop formation waveforms 94 (denoted as94-1, 94-2, 94-3, and 94-4) each have a period 96 and include a pulse98, and each of the drop formation waveforms 92 (denoted as 92-1, 92-2,and 92-3) have a longer period 100 and include a longer pulse 102. Inthis example, the period 96 of the drop formation waveforms 94 is thefundamental period T_(o), and the period 100 of the drop formationwaveforms 92 is twice the fundamental period, 2T_(O). The drop formationwaveforms 94 each cause individual drops to break off from the liquidstream. The drop formation waveforms 92, due to their longer period,each cause a larger drop to be formed from the liquid stream. The largerdrops 54 formed by the drop formation waveforms 92 each have a volumethat is approximately equal to twice the volume of the drops 54 formedby the drop formation waveforms 94.

As previously mentioned, the charge induced on a drop 54 depends on thevoltage state of the charging electrode at the instant of drop breakoff.The B section of FIG. 4 shows the charging electrode waveform 64 and thetimes, denoted by the diamonds, at which the drops 54 break off from theliquid stream 52. The waveforms 92-1, 92-2, 92-3 cause large drops104-1, 104-2, 104-3 to break off from the liquid stream 52 while thecharging electrode waveform 64 is in the second voltage state 84. Due tothe high voltage applied to the charging electrode 62 in the secondvoltage state 84, the large drops 104-1, 104-2, 104-3 are charged to alevel that causes them to be deflected as non-printing drops 68 suchthat they strike the catcher face 74 of the ink catcher 72 in FIG. 3.These large drops may be formed as a single drop (denoted by the doublediamond for 104-1), as two drops that break off from the liquid stream52 at almost the same time that subsequently merge to form a large drop(denoted by two closely spaced diamonds for 104-2), or as a large dropthat breaks off from the liquid stream that breaks apart and then mergesback to a large drop (denoted by the double diamond for 104-3). Thewaveforms 94-1, 94-2, 94-3, 94-4 cause small drops 106-1, 106-2, 106-2,106-3, 106-4 to form. Small drops 106-1 and 106-3 break off during thefirst voltage state 82, and therefore will be relatively uncharged; theyare not deflected into the ink catcher 72, but rather pass by the inkcatcher 72 as printing drops 66 and strike the print media 32 (see FIG.3). Small drops 106-2 and 104-4 break off during the second voltagestate 84 and are deflected to strike the ink catcher 74 as non-printingdrops 68. The charging electrode waveform 64 is not controlled by thepixel data to be printed, while the drop formation waveform 60 isdetermined by the print data. This type of drop deflection is known andhas been described in, for example, U.S. Pat. No. 8,585,189 (Marcus etal.); U.S. Pat. No. 8,651,632 (Marcus); U.S. Pat. No. 8,651,633 (Marcuset al.); U.S. Pat. No. 8,696,094 (Marcus et al.); and U.S. Pat. No.8,888,256 (Marcus et al.), each of which is incorporated herein byreference.

FIG. 5 is a diagram of an exemplary inkjet printhead assembly 112. Theprinthead assembly 112 includes a plurality of jetting modules 200arranged across a width dimension of the print medium 32 in a staggeredarray configuration. The width dimension of the print medium 32 is thedimension in cross-track direction 118, which is perpendicular toin-track direction 116 (i.e., the motion direction of the print medium32). Such printhead assemblies 112 are sometimes referred to as“lineheads.”

Each of the jetting modules 200 includes a plurality of inkjet nozzlesarranged in nozzle array 202, and is adapted to print a swath of imagedata in a corresponding printing region 132. Commonly, the jettingmodules 200 are arranged in a spatially-overlapping arrangement wherethe printing regions 312 overlap in overlap regions 134. Each of theoverlap regions 134 has a corresponding centerline 136. In the overlapregions 134, nozzles from more than one nozzle array 202 can be used toprint the image data.

Stitching is a process that refers to the alignment of the printedimages produced from jetting modules 200 for the purpose of creating theappearance of a single page-width line head. In the exemplaryarrangement shown in FIG. 2, three printheads 200 are stitched togetherat overlap regions 134 to form a page-width printhead assembly 112. Thepage-width image data is processed and segmented into separate portionsthat are sent to each jetting module 200 with appropriate time delays toaccount for the staggered positions of the jetting modules 200. Theimage data portions printed by each of the jetting modules 200 issometimes referred to as “swaths.” Stitching systems and algorithms areused to determine which nozzles of each nozzle array 202 should be usedfor printing in the overlap region 134. Preferably, the stitchingalgorithms create a boundary between the printing regions 132 that isnot readily detected by eye. One such stitching algorithm is describedin commonly-assigned U.S. Pat. No. 7,871,145 (Enge), which isincorporated herein by reference.

The two lines of nozzle arrays 202 in the staggered arrangement areseparated by a nozzle array spacing 138. It has been found that largernozzle array spacing 138 result in large amplitudes of the stitchingvariation, even after stitching correction algorithms are applied.Therefore, it is desirable to reduce the nozzle array spacing 138 asmuch as possible. With prior art arrangements for mounting the nozzlearrays 202, such as that described in the aforementioned,commonly-assigned U.S. Pat. No. 8,226,215 there is a limit to how smallthe nozzle array spacing 138. These methods also get expensive andcumbersome when it is necessary to accommodate larger and larger printwidths. These limitations are addressed with the modular inkjetprinthead assembly described herein.

FIG. 6 shows an exemplary modular printhead assembly 190 including aplurality of printhead modules 260 in accordance with the presentinvention. Each printhead module 260 includes a jetting module 200 and amounting assembly 240. The printhead modules 260 are mounted onto acentral rail assembly 220, which includes a rod 224 attached onto theside of a beam 222 that faces the print medium 32. The print medium 32moves past the printhead assembly 190 in an in-track direction 116. Therail assembly 240 extends across the width of the print medium 32 in across-track direction 118.

In the illustrated configuration, the printhead assembly 190 includesthree printhead modules 260, with one being mounted on a downstream side226 of the rail assembly 220, and two being mounted on an upstream side228 of the rail assembly 220. An advantageous feature of this modularprinthead assembly 190 design is that wider print media 32 can besupported by simply extending the length of the rail assembly 220 andadding additional printhead modules 260. By alternating the printheadmodules 260 between the downstream side 226 and the upstream side 228 ofthe rail assembly 220, the associated nozzle arrays 202 can be stitchedtogether with appropriate overlap regions 134 (see FIG. 5).

FIG. 7 shows additional details for an exemplary embodiment of the railassembly 220 of FIG. 6. The rail assembly 220 includes rod 224, which isattached to the bottom side of beam 222 (i.e., the side that faces theprint medium 32 (FIG. 6). Mounting brackets are attached to the beam 222for used for clamping the mounting assembly 240 to the rail assembly220.

In the illustrated configuration, the rod 224 has a cylindrical shape,and the bottom side of the beam 222 has a concave profile that matchesthe shape of the outer surface of the rod 224. In other configurations,the beam and the rod 224 can have different shapes. For example, thebottom side of the beam 222 can have a v-shaped groove that sits on theouter surface of the rod 224. In another example, the rod 224 can have acylindrical shape around a portion of the circumference, but can have aflat surface on one side to facilitate attaching the rod 224 to a beam222 having a flat bottom side. The rod 224 can be attached to the beam222 using any appropriate means. For example, bolts can be insertedthrough holes in the rod 224 into corresponding threaded holes in thebottom side of the beam 222.

The beam 222 includes a series of notches 223 that are adapted toreceive tabs on the jetting modules 200 and the mounting assemblies 240(FIG. 6) as will be discussed later. In an exemplary embodiment, twonotches 223 are provided for each of the printhead modules 260 (FIG. 6)at locations corresponding to the positions of the tabs, which arepreferably provided in proximity to first and second ends the jettingmodules 200 and the mounting assemblies 240. (Within the context of thepresent disclosure, “in proximity” to an end means that the distancebetween the end and the notch is no more than 20% of the distancebetween the two ends.) In the illustrated configuration, the notches 223extend all the way through the beam 222. In other configurations, thenotches 223 may extend only part of the way through. As will bediscussed later, the beam also includes rotational alignment features225 that are adapted to engage with a corresponding datum on themounting assemblies 240 or the jetting modules 200.

FIG. 8 shows additional details for an exemplary embodiment of thejetting module 200 of FIG. 6. A nozzle array 220 (not visible in FIG. 8)extends across the width of the jetting module 200 in the cross trackdirection 118. Fluid connections 216 and electrical connections 217connect to other components of the printer system 20 (FIG. 1).

The jetting module 200 includes first and second alignment tabs 204, 205spaced apart in the cross-track direction 118 that are configured to beinserted into the notches 223 in the beam 222 and engage with the rod224 of the rail assembly 220 (FIG. 7). In order to define the desiredposition of the jetting module 200 relative to the rail assembly 220requires constraining six degrees of freedom using six alignmentfeatures. The first alignment tab 204 provides a first alignment datum210 and a second alignment datum 211. The second alignment tab 205provides a third alignment datum 212 and a fourth alignment datum 213.The engagement between the first and second alignment tabs 204, 205 withthe rod 224 define four degrees of freedom (x, z, θ_(x), θ_(z)).

The jetting module 200 also includes a rotational alignment featureproviding a fifth alignment datum 214 (not visible in FIG. 8), which isadapted to engage with a corresponding rotational alignment featureassociated with the beam 222 to define the fifth degree of freedom(θ_(y)). The rotational alignment feature associated with the beam 222may be on the beam 222 itself, or can be on the mounting assembly 240,which is in a predefined position relative to the beam 222. In theillustrated configuration, the fifth alignment datum 214 is on thebottom surface of the jetting module 200, and contacts a component ofthe mounting assembly 240 (see FIG. 12B).

The jetting module 200 also includes a cross-track alignment featureproviding a sixth alignment datum 215, which is adapted to engage with acorresponding cross-track alignment feature on the rail assembly 220 todefine the sixth degree of freedom (y). In the illustratedconfiguration, the sixth alignment datum 215 is provided on a side faceof the second alignment tab 205, and the corresponding cross-trackalignment feature on the rail assembly 220 is provided by a side face ofthe corresponding notch 223 in the beam 222. While the sixth alignmentdatum 215 is shown on the inside face of the second alignment tab 205,one skilled in the art will recognize that it could alternatively be onthe outside face. In other configurations, the sixth alignment datum 215can be a side face of the first alignment tab 204, or can be provided bysome other feature on the jetting module 200.

The first and second alignment tabs 204, 205 of the jetting module 200can take any appropriate form. FIGS. 9A-9E illustrate a number ofexemplary configurations that can be used. Each configuration includes a“v-shaped” notch 206, which is formed into the alignment tab 204. Thenotch 206 has two faces 207, 208, each of which provides a correspondingalignment datum 210, 211 at the location where the alignment tab 204contacts the rod 224. In the illustrated examples, the faces 207, 208are oriented at 90° to each other, but this is not a requirement.Fixtures can be provided during the manufacturing process for thejetting module 200 to accurately machine the positions of the faces 207,208 relative to the position of the nozzle array 202, so that the nozzlearray 202 can be accurately aligned relative to the rail assembly 220.

In FIG. 9A the notch 206 has sharp corners and includes a horizontalface 210 and a vertical face 211. The alignment tab 204 of FIG. 9B issimilar except that the outer corners include fillets 201 and the innercorner includes an endmill 203. The alignment tab 204 of FIG. 9Cincludes protrusions 209 which provide the contact points (alignmentdatum 210 and alignment datum 211) with the rod 224. For example, theprotrusions 209 can be ball bearings that provide a single point ofcontact. In FIGS. 9D and 9E the notches 206 are rotates so that thefaces 207, 208 are diagonal. In FIG. 9D, the faces 207, 208 are orientedat ±45° relative to the horizontal. In FIG. 9E, the face 207 tiltsbackward by a small angle (e.g., about 10°). This has the advantage thatthe downward weight of the jetting module 200 will have the effect ofpulling the jetting module 200 toward the rail assembly 220.

FIG. 10 shows additional details for an exemplary embodiment of themounting assembly 240 of FIG. 6. The mounting assembly 240 includesthird and fourth alignment tabs 244, 245 protruding from a frame 242.The alignment tabs 244, 245 are spaced apart in the cross-trackdirection 118 and are configured to be inserted into the notches 223 inthe beam 222 and engage with the rod 224 of the rail assembly 220 (FIG.7). The alignment tabs 244, 245 of the mounting assembly 240 can takeany appropriate form that provides two contact points with the rod 224,such as those shown in FIGS. 9A-9E.

In order to define the desired position of the mounting assembly 240relative to the rail assembly 220 requires constraining six degrees offreedom using six alignment features. The third alignment tab 244provides a seventh alignment datum 250 and an eighth alignment datum251. The fourth alignment tab 245 provides a ninth alignment datum 252and a tenth alignment datum 253. The engagement between the alignmenttabs 244, 245 with the rod 224 therefore define four degrees of freedom(x, z, θ_(x), θ_(z)).

The mounting assembly 240 also includes a rotational alignment featureproviding an eleventh alignment datum 254, which is adapted to engagewith a corresponding rotational alignment feature 225 (FIG. 7) on thebeam 222 to define the fifth degree of freedom (θ_(y)). In theillustrated configuration, the eleventh alignment datum 254 is a ringthat protrudes slightly from the upper cross-piece of the frame 242.

The mounting assembly 240 also includes a cross-track alignment featureproviding a twelfth alignment datum 255, which is adapted to engage witha corresponding cross-track alignment feature on the rail assembly 220to define the sixth degree of freedom (y). In the illustratedconfiguration, the twelfth alignment datum 255 is provided on a sideface of the fourth alignment tab 244, and the corresponding cross-trackalignment feature on the rail assembly 220 is provided by a side face ofthe corresponding notch 223 in the beam 222. While the twelfth alignmentdatum 255 is shown on the outside face of the fourth alignment tab 205,one skilled in the art will recognize that it could alternatively be onthe inside face. In other configurations, the twelfth alignment datum255 can be a side face of the third alignment tab 245, or can beprovided by some other feature on the mounting assembly 240.

A mounting assembly clamping mechanism 310 is used to apply a clampingforce to the mounting assembly 240 clamping it to the rail assembly 220.The clamping force causes the seventh alignment datum 250, the eighthalignment datum 251, the ninth alignment datum 252, and the tenthalignment datum 253 of the mounting assembly 240 to engage with the rod224, and causes the eleventh alignment datum 254 of the mountingassembly 240 to engage with the corresponding alignment feature 225(FIG. 7) on the beam 222. In the illustrated configuration, the mountingassembly clamping mechanism 310 is provided by three bolts 312. One ofthe bolts 312 is shown on one side of the mounting assembly 240 inproximity to the third alignment tab 244. This bolt 312 threads into athreaded hole 316 on the mounting bracket 229 (see FIG. 7), which isattached to the beam 222. Likewise another bolt 312 (not visible in FIG.10) will be on the other side of the mounting assembly 240 in proximityto the fourth alignment tab 245. A third bolt 312 (not shown in FIG. 10)would be inserted through the bolt hole 314 shown in the top rail of theframe 242 and into a threaded hole 318 on the beam 222 at a positioncorresponding to the rotational alignment feature 225 (see FIG. 7). Itwill be obvious to one skilled in the art that a variety of other typesof mounting assembly clamping mechanisms 310 can be used in accordancewith the present invention, including various spring clamp arrangements.

In the illustrated exemplary embodiment, the ink catcher 72 is attachedto the frame 242 of the mounting assembly 240. The charging electrode 62is then attached to the ink catcher 72. A shutter mechanism 352 is alsoattached to the frame 242 of the mounting assembly 240. The shuttermechanism is used to block the path of ink between the nozzles 50 andthe print medium 32 (see FIG. 3) when the jetting module 200 is notbeing used to print image data. Motor 372 is a component of the shuttermechanism 352. The shutter mechanism 352 will be discussed in moredetail later.

A jetting module clamping mechanism 300 is provided for each jettingmodule 200. In the illustrated exemplary embodiment, the jetting moduleclamping mechanism 300 is a component of the mounting assembly 240. Thejetting module clamping mechanism 300 applies a force to the associatedjetting module 200 that causes the first alignment datum 210, the secondalignment datum 211, the third alignment datum 212 and the fourthalignment datum 213 of the associated jetting module 200 to engage withthe rod 224 and causes the fifth alignment datum 214 to engage with acorresponding rotational alignment feature associated with the beam 222.In the illustrated configuration, the fifth alignment datum 214 is onthe bottom surface of the jetting module 200, and contacts acorresponding rotational alignment feature the mounting assembly 240. Ascan be seen in FIG. 12B, the rotational alignment feature in thisexample is on a top surface of the ink catcher 72, which is a componentof the mounting assembly 240, and will therefore have a definedpositional relationship to the beam 222.

In the illustrated exemplary embodiment, the jetting module clampingmechanism 300 is a spring loaded toggle clamp mechanism that can beoperated by a human operator who is installing the jetting module 200into the printhead assembly 190 (FIG. 6). The spring loaded toggle clampmechanism includes a handle 302 connected to two spring plungers 304using a lever mechanism. When the operator lifts the handle 302, the twospring plungers 302 are pushed against corresponding surfaces of thejetting module 200, thereby pushing the jetting module against the railassembly 220. Additional details of the spring loaded toggle clampmechanism can be seen more clearly in FIG. 12D.

A cross-track force mechanism 320 is also provided for each jettingmodule 200. In the illustrated exemplary embodiment, the cross-trackforce mechanism 300 is a leaf spring mechanism which is attached to theframe 242 of the mounting assembly 240. When the jetting module isinserted into the mounting assembly 240, the leaf spring applies across-track force on the jetting module 200 (to the right with respectto FIG. 10), which causes the sixth alignment datum 215 (see FIG. 8) toengage with a corresponding cross-track alignment feature on the beam222. In this case, the inner surface of the second alignment tab 205 ispushed against the side face of the corresponding notch 223 in the beam222. The cross-track force mechanism 320 also serves to apply across-track force on the mounting assembly 240 (to the left with respectto FIG. 10), which causes the twelfth alignment datum 255 to be pushedagainst the side face of the corresponding notch 223 in the beam 222,thereby engaging with a corresponding cross-track alignment feature onthe beam 222. In other configurations, the cross-track force mechanism320 can utilize other types of spring mechanisms, or can utilize anyother type of force mechanisms known in the art that are adapted toprovide a cross-track force (e.g., screw mechanisms, hydraulicmechanisms or toggle clamp mechanisms).

FIG. 11, shows a top view of the printhead assembly 190 of FIG. 6, whichincludes one printhead module 260 mounted on the downstream side 226 ofthe rail assembly 220, and two printhead modules 260 mounted on theupstream side 228 of the rail assembly 220. Some aspects of the variouscomponents can be seen more clearly in this view. The cut-lines areshown corresponding to the views of FIGS. 12A-12D.

FIG. 12A corresponds to cut-line A in FIG. 11, which passes through thecenter of the left-most printhead module 260. FIG. 12B is an enlargedview of the region 380 in FIG. 12A, showing additional details. A numberof features of the printhead assembly 190 can be observed in these view.Slots 350 are provided in the lower surface of each printhead module 260corresponding to the in-track positions of the nozzle arrays 202. Thenozzle array spacing 138 is defined by the in-track distance between thetwo slots 350. As discussed earlier, it is desirable to minimize thenozzle array spacing 138 to reduce stitching errors. An advantage of theexemplary embodiment of printhead assembly 190 is that the slots 350 canbe positioned quite close to the rail assembly 220. This is partiallydue to the fact that the ink catcher 72 is positioned upstream of thenozzle array 202 for the jetting module 200 on the upstream side 228 ofthe rail assembly 220, and the ink catcher 72 is positioned downstreamof the nozzle 202 array for the jetting module 200 on the downstreamside of the rail assembly 220. Because the ink catchers 72 extend out asignificant distance from the nozzle arrays 202, prior art system wherethe ink catchers 72 were all positioned on the same side of the nozzlearrays 202 required that the nozzle array spacing 138 be significantlylarger.

The eleventh alignment datum 254 on the frame 242 of the mountingassembly 240 can also be seen. The mounting assembly clamping mechanism310 (FIG. 10), pushes the alignment datum 254 into a correspondingrotational alignment feature 256 on the beam 222 of the rail assembly220.

FIG. 12B shows an enlargement of the region 380 in FIG. 12A, and moreclearly illustrates the portion of the printhead assembly 190 in thevicinity of the nozzle array 202. Undeflected printing drops 66 passthrough a slot 350 formed between air guide 368 and the lower plate 79of the ink catcher 72. Repositionable shutter blade 356 can beselectively repositioned to block the slot 350, as will be discussed inmore detail later. The liquid channel 78 of the ink catcher 72 drawsaway non-printing drops 68 (FIG. 4) for recycling. In the illustratedconfiguration, the fifth alignment datum 214 of the jetting module 200is provided by a protrusion which extends from the lower surface of thejetting module. The fifth alignment datum 214 contacts an upper surfaceof the ink catcher 72, which provides the rotational alignment feature256. The ink catcher 72 is a component of the mounting assembly 240,which is mounted onto the rail assembly 220 in a predefined location,with the rotational alignment being defined relative to the beam 222 ashas been discussed earlier. The rotational alignment feature 256 istherefore indirectly associated with the beam 222, even though it is notdirectly on the beam 222. In other embodiments, the fifth alignmentdatum 214 can be located in a different position on the jetting module200. For example, the fifth alignment datum 214 can be a protrusion onthe face of the jetting module that faces the beam 222. The rotationalalignment feature 225 can then be a point on the beam 222, or on theframe 242 (FIG. 10) of the mounting assembly 240.

FIG. 12C corresponds to cut-line B in FIG. 11, which passes throughalignment tab 244 of the mounting assembly 240 in the left-mostprinthead module 260 in FIG. 11 (i.e., the upstream printhead module 260on the right-hand side of FIG. 12C). It can be seen that the alignmenttab 244 is inserted partway through the notch 223 in beam 222, and thatthe seventh alignment datum 250 and the eighth alignment datum 251 arein contact with the rod 224.

FIG. 12D corresponds to cut-line C in FIG. 11, which passes through thealignment tab 204 of the jetting module 200 in the left-most printheadmodule 260 in FIG. 11 (i.e., the upstream printhead module 260 on theright-hand side of FIG. 12C). Cut-line C also passes through the springplunger 304 of the upstream printhead module 260. The handle 302 of thejetting module clamping mechanism 300 for the upstream printhead module260 has been pushed upward into the engaged position, so that the springplunger 304 is applying a force onto an angled surface along one side ofthe jetting module 200. This pushes the alignment tab 204 of the jettingmodule 200 tightly against the beam 222 of the rail assembly 220. It canbe seen that the alignment tab 204 is inserted partway through the notch223 in beam 222, and that the first alignment datum 250 and the secondalignment datum 251 are in contact with the rod 224. A second springplunger 304 (not visible in FIG. 12D) is similarly applying a force ontoan angled surface along the other side of the jetting module 200,thereby engaging the second alignment tab 205 with the rod 224. Adownward component of the force provided by the jetting module clampingmechanism 300 also pushes downward on the jetting module 200 so that thefifth alignment datum 214 engages with the corresponding rotationalalignment feature 256 on the mounting assembly 240 (as discussed withrespect to FIG. 12B). The handle 302 of the jetting module clampingmechanism 300 for the downstream printhead module 260 on the left sideof FIG. 12D has been pushed downward into the released position, so thatthe spring plungers 304 have been pulled away from the jetting module200. This enables the jetting module 200 to be extracted from theprinthead assembly 190 (e.g., for maintenance).

FIG. 13A shows a side view of the printhead assembly 190 of FIG. 6 asviewed from the downstream side 226. One printhead module 260 is visibleon the downstream side 226 of the rail assembly 220, with the other twoprinthead modules 260 being behind the rail assembly 220 on the upstreamside 228 (FIG. 6).

FIG. 13B shows an enlargement of the region 382 in FIG. 13A, and moreclearly illustrates the portion of the printhead assembly 190 in thevicinity of the one of the notches 223 in the beam 220. Alignment tab245 of the mounting assembly 240 (see FIG. 10) and alignment tab 205 ofthe jetting module 200 (see FIG. 8) in the left printhead module 260behind the rail assembly 220 are visible within the notch 223. The leafspring which serves as the cross-track force mechanism 320 (see FIG. 10)is visible between the alignment tabs 205, 245. The cross-track forcemechanism 320 applies a cross-track force to both the mounting assembly240 and the jetting module 200.

In the illustrated exemplary embodiment, the cross-track force mechanism320 pushes the mounting assembly 240 to the left so that the alignmentdatum 255 on the outer face of the alignment tab 245 contacts the leftface of the notch 223, which serves as the corresponding cross-trackalignment feature associated with the beam 222. As discussed earlier, inother embodiments, other features on the mounting assembly 240 can serveas the alignment datum 245.

Similarly, in the illustrated exemplary embodiment, the cross-trackforce mechanism 320 pushes the jetting module 200 to the right so thatthe alignment datum 215 on the inner face of the second alignment tab205 contacts the right face of the notch 223, which serves as thecorresponding cross-track alignment feature associated with the beam222.

In other embodiments, other features on the jetting module 200 can serveas the alignment datum 215. For example, the alignment datum 215 can beon outer face of the first alignment tab 204. As the cross-track forcemechanism 320 pushes the jetting module 200 to the right, the spacingbetween the alignment tabs 204, 205 and the spacing between thealignment tabs 244, 245 can be arranged such that the outer face of thefirst alignment tab 204 comes into contact with the inner face of thethird alignment tab 244 (see FIG. 10) on the mounting assembly 240. Inthis case, the inner face of the alignment tab 244 serves as thecorresponding cross-track alignment feature associated with the beam222. Since the mounting assembly 240 is mounted onto the rail assembly220 in a predefined location, with the cross-track alignment beingdefined relative to the beam 222 as has been discussed earlier, thecross-track alignment feature on the alignment tab 244 is thereforeindirectly associated with the beam 222, even though it is not directlyon the beam 222.

FIG. 14 is an exploded view showing components of the shutter mechanism352 according to an exemplary embodiment. The shutter mechanism 352includes a shutter frame 354, and a repositionable shutter 355. In anexemplary configuration, the shutter frame 354 is adapted to be mountedto the mounting assembly 240 (see FIG. 10), and the repositionableshutter 355 is mounted to the shutter frame 354 using shafts 366 whichenable the repositionable shutter 355 to pivot about a pivot axis 362.In other configurations, the shutter mechanism 352 can be mounted toother components of the printhead module 260 (e.g., the jetting module200). Preferably, the shutter mechanism 352 is detachable from theprinthead module 260 so that it can be removed for maintenance (e.g.,cleaning) or replacement.

The repositionable shutter 355 includes a shutter blade 356 extending inthe cross-track direction 118 from a first end to a second end. Tabs 358are affixed to the first and second ends of the shutter blade 356. Inthe illustrated exemplary embodiment, both tabs 358 include lever arms360, which are adapted to be pushed downward to rotate therepositionable shutter 355 around the pivot axis 362. When therepositionable shutter 355 is pivoted into a first pivot position, theshutter blade 356 blocks drops of ink from passing through the slot 350(see FIG. 12B) and diverts the ink into the ink catcher 72. When therepositionable shutter 355 is pivoted into a second pivot position, theshutter blade 356 is moved away from the slot 350 so that drops of inkcan pass through the slot 350. In a preferred configuration, the shutterblade 356 includes an elastomeric tip 357 adapted to seal against thelower plate 79 of the ink catcher 72 when the repositionable shutter 355is in the first pivot position (see FIG. 16B).

In the illustrated exemplary configuration, the tabs 358 includecircular holes 364 coaxial with the pivot axis 362. The shafts 366 areadapted to be mounted into holes 365 in the shutter frame 354 and extendinto the holes 364 in the tabs 358 such that the shafts 366 and theholes 364, 365 are all coaxial with the pivot axis 362. In someconfigurations, the shafts 366 can be affixed to the shutter frame 354,so that the repositionable shutter 355 pivots around the shafts 366. Inother configurations, the shafts 366 can be affixed to therepositionable shutter 355, so that the shafts 366 pivot together withthe repositionable shutter 355. In the illustrated configuration, theholes 364 extend all the way through the tabs 358 and the holes 365extend all the way through the tabs on the shutter frame 354. In otherconfigurations, some or all of the holes 364, 365 may extend onlypartway through their respective tabs.

In the illustrated exemplary configuration, an air guide 368 is mountedto the shutter frame 354. When the shutter mechanism 352 is attached tothe mounting assembly 240 (see FIG. 10), the air guide 368 is positionedto direct a stream of air from an air supply (not shown) downwardthrough the slot 350 (see FIG. 12B). This is useful to keep the drops ofink from slowing down during their flight from the nozzle array 202 tothe slot 350. In a preferred configuration, the air guide 368 definesone side wall of the slot 350, while the ink catcher 72 defines theother side wall (see FIG. 12B). In the illustrated configuration, theair guide 368 includes tabs 369 on both ends which define end walls forthe slot 350.

Springs 369 are positioned between the shutter frame 354 and the shutterblade 356. The springs provide a restoring force that opposes thedownward force on the lever arm 360 to pivot the repositionable shutter355 back into the first pivot position with the downward force on thelever arm 360 is removed.

FIG. 15 shows the components of the shutter mechanism 352 of FIG. 14 inan assembled position. In this case, the repositionable shutter 355 isshown in the first pivot position where the shutter blade 356 ispositioned to block the slot 350 (FIG. 12B).

As discussed earlier, the shutter mechanism 352 is adapted to beoperated by applying a force onto the lever arm 360 of therepositionable shutter 355. This can be accomplished with an actuator370 as illustrated in FIGS. 16A-16B. In the illustrated exemplaryconfiguration, the actuator 370 includes a motor 372 which rotates alever 373 mounted onto a shaft 372 of the motor 372. The lever 371 canbe rotated between a first position shown in FIG. 16A and a secondposition shown in FIG. 16B. The lever 371 is attached to a push rod 374.The push rod 374 is adapted to pivot a pivoting lever 375 around a pivotpoint 376. The pivoting lever 375 is adapted to apply a downward forceonto the lever arm 360 of the repositionable shutter 355.

When the actuator 370 is in the first position shown in FIG. 16A, thepivoting lever 373 is moved away from the lever arm 360 of therepositionable shutter 355. The springs 360 of the shutter mechanism 352pivot the repositionable shutter 355 into the first pivot position whichblocks the slot 350.

When the actuator 370 is in the second position shown in FIG. 16B, thepivoting lever 373 is pushed downward onto the lever arm 360 of therepositionable shutter 355. This pivots the repositionable shutter 355into the second pivot position which opens the slot 350.

In a preferred configuration, when power is applied to the actuator 370(e.g., to the motor 371), the repositionable shutter 355 is pivoted fromthe closed first pivot position to the open pivot position, and when thepower is turned off the repositionable shutter 355 returns to the closedfirst pivot position. This has the advantage that if the printer system20 (FIG. 1) experiences a power failure, the repositionable shutter 355will close providing a failsafe feature which prevents ink from flowingthrough the slot 350 onto the print medium 32.

As was discussed relative to FIG. 14, in some embodiments therepositionable shutter 355 includes lever arms 360 on both ends of theshutter blade 356. In this case, the actuator 370 can be configured tosimultaneously apply a downward force to both lever arms 360. In anexemplary configuration, the motor 371 is positioned at a cross-trackposition intermediate to the two ends of the shutter blade as shown inFIG. 10. A rod 377 extends from the lever 373 to push rods 374 (FIG.16A) located along both edges of the mounting assembly 240. The pushrods 374 each connect to respective pivoting levers 375, which activaterespective lever arms 360 of the shutter blade 356. In an alternateconfiguration (not shown) two separate actuators 370 are used to actuatethe two lever arms 360. In other configurations, a single actuator 370can be used to actuate a single lever arm 360 on one end of the shutterblade 356. However, this requires that the shutter blade 356 havesufficient stiffness so that it will not twist significantly duringactuation.

FIGS. 17A-17B illustrate additional details about the operation of therepositionable shutter 355. In FIG. 17A, the repositionable shutter 355is pivoted into the first pivot position where the shutter blade 356blocks the slot 350. In this position, the elastomeric tip 357 of theshutter blade 356 seals against the lower plate 79 of the ink catcher72. This redirects any printing drops 66 into the liquid channel 78 ofthe ink catcher.

In FIG. 17B, a force F is applied onto the lever arm 360 of the tab 358by the actuator 370 (see FIG. 16A). This causes the repositionableshutter 355 to pivot around the pivot axis 362, pivoting therepositionable shutter 355 into the second pivot position where theshutter blade 356 is pulled back from the slot 350, allowing printingdrops 66 to reach the print medium 32.

The pivot axis 362 is preferably positioned between the nozzle array 202and the slot 350. This enables the shutter blade 356 to be efficientlypulled back from the slot 350 with a relatively small angular rotationof the repositionable shutter 355. It also enables the shutter mechanism352 to be compact, thereby enabling the distance between the nozzlearray 202 and the rail assembly 220 to be reduced in order to minimizethe nozzle array spacing 138 (see FIG. 12A).

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

PARTS LIST

-   20 printer system-   22 image source-   24 image processing unit-   26 control circuits-   27 synchronization device-   28 drop forming transducer-   30 printhead-   32 print medium-   34 print medium transport system-   35 speed measurement device-   36 media transport controller-   38 micro-controller-   40 ink reservoir-   44 ink recycling unit-   46 ink pressure regulator-   47 ink channel-   48 jetting module-   49 nozzle plate-   50 nozzle-   51 heater-   52 liquid stream-   54 drop-   55 drop formation waveform source-   57 trajectory-   59 breakoff location-   60 drop formation waveform-   61 charging device-   62 charging electrode-   62′ charging electrode-   63 charging electrode waveform source-   64 charging electrode waveform-   66 printing drop-   68 non-printing drop-   69 drop selection system-   70 deflection mechanism-   71 deflection electrode-   72 ink catcher-   74 catcher face-   76 ink film-   78 liquid channel-   79 lower plate-   80 charging electrode waveform 64 period-   82 first voltage state-   84 second voltage state-   86 non-print trajectory-   88 print dot-   92 drop formation waveform-   94 drop formation waveform-   96 period-   98 pulse-   100 period-   102 pulse-   104 large drop-   106 small drop-   108 phase shift-   112 printhead assembly-   116 in-track direction-   118 cross-track direction-   132 printing region-   134 overlap region-   136 centerline-   138 nozzle array spacing-   190 printhead assembly-   200 jetting module-   201 fillet-   202 nozzle array-   203 endmill-   204 alignment tab-   205 alignment tab-   206 notch-   207 face-   208 face-   209 protrusion-   210 alignment datum-   211 alignment datum-   212 alignment datum-   213 alignment datum-   214 alignment datum-   215 alignment datum-   216 fluid connections-   217 electrical connections-   220 rail assembly-   222 beam-   223 notch-   224 rod-   225 rotational alignment feature-   226 downstream side-   228 upstream side-   229 mounting bracket-   240 mounting assembly-   242 frame-   244 alignment tab-   245 alignment tab-   250 alignment datum-   251 alignment datum-   252 alignment datum-   253 alignment datum-   254 alignment datum-   255 alignment datum-   256 rotational alignment feature-   260 printhead module-   300 jetting module clamping mechanism-   302 handle-   304 spring plunger-   310 mounting assembly clamping mechanism-   312 bolt-   314 bolt hole-   316 threaded hole-   318 threaded hole-   320 cross-track force mechanism-   350 slot-   352 shutter mechanism-   354 shutter frame-   355 repositionable shutter-   356 shutter blade-   357 elastomeric tip-   358 tab-   360 lever arm-   362 pivot axis-   364 hole-   365 hole-   366 shaft-   369 spring-   368 air guide-   369 tab-   370 actuator-   371 motor-   372 shaft-   373 lever-   374 push rod-   375 pivoting lever-   376 pivot point-   377 bar-   380 region-   382 region

The invention claimed is:
 1. An inkjet printhead assembly including aremovable jetting module for printing on a print medium traveling alonga media path from upstream to downstream, comprising: a rail assemblyspanning the print medium in the cross-track direction including: abeam; and a rod attached to a side of the beam that faces the printmedium; a printhead module including: a jetting module having an arrayof nozzles extending in a cross-track direction, wherein the jettingmodule includes: a first alignment tab having a first alignment datumand a second alignment datum; a second alignment tab having a thirdalignment datum and a fourth alignment datum, the second alignment tabbeing spaced apart from the first alignment tab in the cross-trackdirection; a rotational alignment feature including a fifth alignmentdatum; and a cross-track alignment feature including a sixth alignmentdatum; and a mounting assembly adapted to engage with the rail assemblyat a defined cross-track position including: a third alignment tabhaving a seventh alignment datum and an eighth alignment datum; a fourthalignment tab having a ninth alignment datum and a tenth alignmentdatum, the fourth alignment tab being spaced apart from the thirdalignment tab in the cross-track direction; a rotational alignmentfeature including an eleventh alignment datum; a jetting module clampingmechanism for applying a force to the jetting module that causes thefirst alignment datum, the second alignment datum, the third alignmentdatum and the fourth alignment datum of the jetting module to engagewith the rod, and causes the fifth alignment datum of the jetting moduleto engage with corresponding rotational alignment feature associatedwith the beam; and a mounting assembly clamping mechanism for applying aforce to the mounting assembly that causes the seventh alignment datum,the eighth alignment datum, the ninth alignment datum, and the tenthalignment datum of the mounting assembly to engage with the rod, andcauses the eleventh alignment datum of the mounting assembly to engagewith a corresponding alignment feature on the beam; and a jetting modulecross-track force mechanism for applying a cross-track force to thejetting module that causes the sixth alignment datum of the jettingmodule to engage with a corresponding cross-track alignment featureassociated with the beam; wherein portions of the first and secondalignment tabs of the jetting module and portions of the third andfourth alignment tabs of the mounting assembly are adapted to fit withincorresponding notches in the beam.
 2. The inkjet printhead assembly ofclaim 1, wherein the first and second alignment tabs include a notchhaving two faces, the first alignment datum and the second alignmentdatum corresponding to locations on the faces of the notch in the firstalignment tab that contact the rod, and the third alignment datum andthe fourth alignment datum corresponding to locations on the faces ofthe notch in the second alignment tab that contact the rod.
 3. Theinkjet printhead assembly of claim 2, wherein the notches are v-shaped.4. The inkjet printhead assembly of claim 1, wherein the sixth alignmentdatum is a feature on the first alignment tab or the second alignmenttab.
 5. The inkjet printhead assembly of claim 4, wherein the sixthalignment datum is a side face of the first alignment tab or the secondalignment tab, and wherein the cross-track alignment feature is a sideface of the corresponding notch in the beam.
 6. The inkjet printheadassembly of claim 1, wherein the jetting module cross-track forcemechanism is a spring mechanism that applies the cross-track force tothe jetting module.
 7. The inkjet printhead assembly of claim 1, whereinthe jetting module cross-track force mechanism is a component of themounting assembly or is mounted on the mounting assembly.
 8. The inkjetprinthead assembly of claim 1, wherein the rotational alignment featureassociated with the beam that engages with the fifth alignment datum ofthe jetting module is a feature of the mounting assembly having apredefined position relative to the beam.
 9. The inkjet printheadassembly of claim 1, wherein the printhead module includes an inkcatcher for catching non-printing drops of ink ejected from the array ofnozzles, the ink catcher being mounted to the mounting assembly.
 10. Theinkjet printhead assembly of claim 9, wherein drops of ink ejected fromthe array of nozzles pass through a slot before they impinge on theprint medium, and wherein the printhead module includes a repositionableshutter blade that can be positioned to block drops of ink from passingthrough the slot and divert the ink into the ink catcher, therepositionable shutter blade being mounted to the mounting assembly. 11.The modular inkjet printhead assembly of claim 9, wherein the inkcatcher is positioned upstream of the array of nozzles for jettingmodules engaging with the rail assembly on the upstream side of the railassembly, and the ink catcher is positioned downstream of the array ofnozzles for jetting modules engaging with the rail assembly on thedownstream side of the rail assembly.
 12. The inkjet printhead assemblyof claim 1, wherein the printhead module includes a charging module forapplying a charge to drops of ink ejected from the array of nozzles, thecharging module being mounted to the mounting assembly.
 13. The inkjetprinthead assembly of claim 1, wherein the mounting assembly includes amounting assembly cross-track alignment feature including a twelfthalignment datum, and further including a mounting assembly cross-trackforce mechanism for applying a cross-track force to the mountingassembly that causes the twelfth alignment datum to engage with acorresponding cross-track alignment feature associated with the beamthereby positioning the mounting assembly at the defined cross-trackposition.
 14. The inkjet printhead assembly of claim 1, wherein the rodhas a cylindrical shape around at least a portion of its circumference.15. The inkjet printhead assembly of claim 1, wherein the jetting moduleclamping mechanism includes a spring loaded toggle clamp that can beoperated by a human operator to apply the force to the associatedjetting module.
 16. The inkjet printhead assembly of claim 1, whereinthe first tab is located in proximity to a first end of the jettingmodule, and the second tab is located in proximity to an opposing secondend of the jetting module.